[time-nuts] Data collection cycle -- multiple sources
toonecounter?
Poul-Henning Kamp
phk at phk.freebsd.dk
Sun Jun 19 13:41:44 EDT 2005
In message <42B5AC9A.20305 at onetel.net>, David Kirkby writes:
>The attenuator will reduce a 1W source to 250mW (6dB attenuation).
>Assuming the load on the output of the attenuator is open or short (so
>100% reflection), the power will be reduced by another factor of 4 (to
>62.5mW) before it reaches the source. So only 6.25% is reflected back to
>the source. That's a VSWR of less than 1.7.
Be aware that there is a big difference in impact on square and sine
signals.
Even a minor change in circumstances will push the zero-crossing of a
sine wave signal one way or the other. This is because (compared to
a square-wave) the slope at the zero-crossing is very low in terms
of V/s.
Also, if measuring squarewave signals, be sure to choose your trigger
point wisely. Many digital drivers control for the V(il)/V(ih) voltages
and neither is likely to be V(max)/2.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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